This invention relates to novel nematic compounds which have a negative anisotropy of the dielectric constant (DC) and are suitable as components for liquid crystal (LC) mixtures. This invention also relates to nematic LC mixtures which contain the novel compounds as components and have an overall negative DC anisotropy.
Nematic liquid crystal mixtures with negative dielectric constant anisotropy (DCA) are required for operating certain displays, for example for the so-called guest/host displays (GHD) and homotropic-nematic displays (HND) with a positive image display or positive contrast. Similar compounds are known, for example from J. C. Dubois et al., Mol. Cryst. Liq. Cryst. 42 [1977] 139; German Offenlegungschriften No. 2,240,864, 2,613,293, 2,835,682, and 2,937,700, Soviet Patent Specification No. 562,547 and European patent application No. 80200464.8).
However, no satisfactory nematic LC mixtures, which have a sufficiently strong negative DCA (for example 2 or better) in combination with the further properties, necessary for perfect operation of display cells, of LC mixtures, such as chemical stability in general, photochemical, electrochemical and thermal stability, and a sufficiently wide range of anisotropy as well as sufficiently short response times even at low temperatures, for example at most about one second at the lower end of the anisotropy range, are yet obtainable by means of the compounds hitherto known.